This invention relates to a workpiece feeding apparatus in a seam welding machine for automating a seam welding operation on a workpiece such as a fuel tank for a two-wheeled vehicle or the like.
It has been usual hitherto that, when a workpiece is to be Mig or Tig welded, the workpiece is fixed and the welding is carried out by a welding torch moved by a robot. However, if a seam welding is intended to carried out under the condition that the workpiece is fixed, a welding unit of comparatively large weight comprising a pair of electrode rolls, a pressure applying mechanism and a rotation driving mechanism must be mounted on a robot. As a result, the working speed of the robot becomes slow. Consequently, the productivity of the welded workpieces becomes low.
Alternatively, such an arrangement can be considered that a stationary type seam welding machine installed on a floor is used, and the workpiece is moved by a robot so that a portion of the workpiece to be welded is fed between a pair of electrode rolls provided on the seam welding machine. However, with this arrangement, in a case where it is applied to the portion to be welded which is three-dimensionally curved, such as a butt flange portion c of a tank outer panel a and a tank bottom panel b of a fuel tank A for a two-wheeled vehicle as shown in FIG. 3, three-dimensional movement control of the workpiece and a posture control thereof are required.
If, in this case, the robot is installed on a floor, an installation floor space for the entire apparatus including the seam welding machine is increased. In addition, cooling water applied to the workpiece is liable to be applied also to the robot, and there is fear of generation of rust or other bad effect thereon.